Coronary artery disease results in a narrowing of the coronary arteries, which are the blood vessels that supply the heart with oxygen and nutrients. There are two main coronary arteries: the left main coronary artery, which supplies blood to the left ventricle, and the right main coronary artery, which supplies blood to the right ventricle as well as the posterior surface of the left ventricle. These main coronary arteries give rise to several branches that extend into the heart muscle (myocardium), bringing vital nutrients to each muscle cell. The heart relies on these nutrients as it works constantly to pump blood through the body. Narrowing of the coronary arteries reduces blood flow to the myocardium and, if untreated, can damage and/or destroy the heart muscle.
In some cases, coronary artery disease may be treated by the use of drugs and/or by modifications in behavior and diet. For certain patients, however, a coronary artery bypass graft (CABG) procedure is the preferred form of treatment to restore adequate blood flow. A CABG procedure improves the flow of blood and ensures that the heart muscle is receiving an adequate supply of oxygen-rich blood.
In a CABG procedure, a blocked section of the artery is literally “bypassed” by attaching a healthy segment of blood vessel downstream from the diseased or blocked area. During surgery, an incision is made in the patient's chest and the sternum is divided to allow access to the pericardial sac, which envelops and protects the heart.
Some CABG procedures can be performed with a beating heart, while others require that the heart be arrested, usually by administering a chemical solution, called cardioplegia, that temporarily paralyzes the heart muscle fibers. In procedures where the heart is arrested, circulation is maintained by a heart-lung machine.
During the procedure, manual manipulation and repositioning of the heart is usually necessary to access the blocked arteries. The posterior descending artery, for example, lies on the posterior surface of the heart. The surgeon or a surgical assistant is therefore required to lift and rotate the heart to expose the artery. Often, a surgeon uses his or her own hands to position the heart. However, it is difficult to maintain the heart in a secure and proper position by such techniques. In addition, direct manual contact with the heart may impair circulation, leading to reductions in cardiac output and blood pressure. Care must be exercised to avoid trauma to the heart or pericardial sac to avoid the formation of excessive adhesions.
In order to overcome these problems, devices such as slings and balloons have been developed to help position and/or stabilize the heart. A balloon, for example, is placed underneath the heart and is thereafter inflated to lift the heart into a desired position. A sling, on the other hand, is a fabric or plastic based device that is placed around the heart in the manner of a hammock. The heart can then be positioned by moving the sling.
While attempts have been made to support the heart during a CABG surgery, the resulting devices and techniques have several drawbacks that have hindered their acceptance in the art. For example, slings made of net or fabric tend to interfere with access to the surgical target. Moreover, net slings require special techniques or procedures to remove the net from the surgical target area. Where a balloon is employed, the heart is freely slidable on the balloon, and not necessarily securely positioned, thus posing a risk of damage during the surgical procedure. Moreover, if a balloon is over-inflated, it can exert excess pressure on the heart, potentially causing damage to the heart.
In addition to the aforementioned problems, the recent trend in moving toward less invasive procedures makes placement of a sling or inflatable balloon nearly impossible. A minimally invasive cardiac surgery (MICS) procedure is a new technique which, compared with standard cardiac procedures, causes less pain, speeds recovery, and delivers identical results at less cost.
MICS procedures are usually performed on the beating heart, thereby eliminating the expense and risk of stopping the heart and the necessity of a heart-lung bypass machine. The procedure is performed by making an incision in the chest (thorocotomy). A heart stabilizer can be used to restrict movement of the heart within the limited surgical field.
Since the surgeon is operating on a beating heart, both movement and blood can cause a sling or balloon to displace during surgery. Moreover, the surgeon's ability to access and manipulate the heart is hampered since the incision used to access the thoracic cavity is much smaller. As a result, the limited surgical field makes placement of any type of inflatable balloon or sling around the heart very difficult.
Surgeons have also employed retraction sutures and retraction tapes to lift and secure the heart during surgical procedures. In one technique a number of retraction sutures (e.g., three) are placed deep within the pericardium and then tensioned to lift the heart. In another technique, retraction tapes, which are usually thick, porous straps, are placed strategically around the heart. The tapes are then gradually retracted to reposition the heart and expose the target artery. Typically, two pairs of retraction tapes are employed. The first pair is passed through the transverse sinus, and the second pair is passed beneath the inferior vena cava. One end of each tape is fixed to a stationary support and the other end of each tape is kept free. The free ends can then be retracted to position the heart. Once the heart is in the desired position, the free ends of the tapes can be secured to the support.
The use of retraction sutures and retraction tapes has some drawbacks in that it is difficult and time consuming to place these devices properly while avoiding risk of damage to the heart.
For example, when sutures are used, the tip of the suture needle must be placed along the pericardium, and then rotated to penetrate through the tissue. Unpredictable motion of the epicardial surface during needle placement may cause laceration of the heart or puncture of a coronary artery. A high degree of skill is also required to grasp the proper amount of tissue. If an insufficient amount of tissue is engaged, the suture may tear through the tissue and fail. Conversely, if too much tissue is engaged, the suture may penetrate and possibly damage an underlying organ, such as the lung.
The proper placement of retraction tapes is made difficult due to the limited surgical field and reduced field of vision. Moreover, the procedure can be time consuming and risky since a pair of retraction tapes needs to be placed through the transverse sinus. Traumatic stressing of the transverse sinus, or excessive destruction of the tissue, can lead to stenosis, further compromising the patient's health. Further, the placement of retraction tapes directly around the heart can lead to a significant drop in blood pressure.
Accordingly, there is a need for an organ positioning and manipulating device which can be easily, quickly, and safely employed to present and expose target surgical tissue.